If I understand you correctly. You want to get rid of an virus that modifies the BIOS and/or CMOS. Well most motherboards come with Virus detection build-in. What virus are you thinking off?
I've not heared of any new ones lately, but I would suggest that the first step is running your AV software.
The second step, if your AV doesn't find it is to update your definitions,
The third step is to scan again
if your AV can't get rid of something, the next best friend is often Google
I would guess that generally when all else fails, if you can get rid of, or prevent the file(s) sending the virus to memory from ever executing on your next reboot, then it's just a matter of getting rid of the infection itself.